Adhesive-applying apparatus

ABSTRACT

A flowable adhesive is applied to a carton blank or paper web by an application nozzle, having a discharge orifice, which is permanently open to ambient pressure. The nozzle is divided into two compartments which are interconnected adjacent to the orifice. One compartment is connected to an adhesive container by a feed conduit and the other is connected to the container by a return conduit. Adhesive is continuously fed by a pump, at a predetermined pressure higher than ambient pressure from the container to the nozzle and returned to the container by a separate suction pump, so that no adhesive is ejected through the orifice. In order that adhesive may be ejected the pressue in the feed conduit is increased, at the required times by means of a piston which displaces adhesive from a cylinder which is in communication with the feed conduit. In a modified form the nozzle comprises coaxial inner and outer tubes the inner tube being adjustable axially relative to the outer tube. By suitably adjusting the two pumps and the difference in level between the ends of the tubes, adhesive may either be caused to flow continuously from the nozzle or intermittently, by increasing the pressure in the feed conduit.

United States Patent [191 Davies et al.

[451 June 11, 1974 1 ADHESIVE-APPLYING APPARATUS [75] Inventors: Robert William Davies; Leonard Thornton, both of Deptford, England [73] Assignee: Molins Limited, London, England [22] Filed: Nov. 20, 1972 [21] Appl. No.: 308,097

[52] US. Cl 239/125, 118/603, 222/318 [51] Int. Cl B051) l/32 [58] Field of Search 239/124, 125, 126, 127,

[56] References Cited UNITED STATES PATENTS 2,469,786 9/1969 Holland 239/126 2,727,786 12/1955 3,023,968 3/1962 3,524,587 8/1970 3,537,653 ll/l970 3,590,775 7/1971 Barr 239/127 X Primary Examiner-M. Henson Wood, Jr. Assistant Examiner--Michael Y. Mar Attorney, Agent, or Firm-Markva & Smith 57 ABSTRACT A flowable adhesive is applied to a carton blank or paper web by an application nozzle, having a discharge orifice, which is permanently open to ambient pressure. The nozzle is divided into two compartments which are interconnected adjacent to the orifice. One compartment is connected to an adhesive container by a feed conduit and the other is connected to the container by a return conduit.

Adhesive is continuously fed by a pump, at a predetermined pressure higherthan ambient pressure from the container to the nozzle and returned to the container by a separate suction pump, so that no adhesive is ejected through the orifice. In order that adhesive may be ejected the pressue in the feed conduit is increased, at the required times by means of a piston which displaces adhesive from a cylinder which is in communication with the feed conduit.

In a modified form the nozzle comprises coaxial inner and outer tubes the inner tube being adjustable axially relative to the outer tube. By suitably adjusting the two pumps and the difference in level between the ends of the tubes, adhesive may either be caused to flow continuously from the nozzle or intermittently, by increasing the pressure in the feed conduit.

19 Claims, 9 Drawing Figures PATENTEDJUNH I914 3.8151822 SHEET 10$ 5 PATENTEDJUN 1 1 mm SHEET 2 OF 5 QR S ADHESIVE-APPLYING APPARATUS This invention concerns improvements in or relating to apparatus for applying liquids (e.g. flowable adhesive) to a surface, e.g. a carton blank, or a web of paper or the like.

In one form of known apparatus for applying flowable adhesive to a surface the adhesive is fed under pressure from a tank along a pipe to an applicator nozzle having a closure member at its outlet which is pushed back against a spring into the nozzle to open the outlet .and allow adhesive to flow out onto the surface.

In a further known form of apparatus hot melt adhesive is fed continuously under pressure from a tank along a pipe to at least one applicator nozzle and then back to the tank, the nozzles being normally closed. When it is desired to eject adhesive from the nozzles the pressure in the pipe is increased, by restricting the flow of adhesive back into the tank, which causes the nozzles to open.

According to the present invention there is provided apparatus for applying a liquid, for example a flowable adhesive or the like to a surface, comprising a container for the liquid, at least one applicator nozzle, feed and return conduits for conveying liquid from the container to the nozzle and from the nozzle to the container respectively, and means for circulating liquid continuously from the container through said conduits, in which said nozzle has a discharge orifice which is in communication with said conduits and is permanently open.

It will be appreciated that although such apparatus may be used in conditions in which the ambient pressure is above or below atmospheric pressure, it is more usual to use the apparatus in conditions of substantially atmospheric pressure.

In such apparatus while the pressure of liquid at the nozzle is substantially ambient no liquid is ejected through the orifice; in general, the liquid is kept in circulation so that it remains in a suitable flowable state, but a small quantity of liquid may be stationary in the orifice. It is preferred to have the nozzle of such form that the effective length of the orifice is asshort as possible, so that no substantial quantity of liquid is stationary therein. In a preferred form, the nozzle includes separate feed and return passages connected to the feed and return conduits respectively, said passages being interconnected immediately adjacent to the inner end of the orifice. Said passages may extend through substantially the whole length of the nozzle.

The liquid circulating means may comprise a first pump for feeding the liquid continuously at a predetermined pressure above ambient pressure along said feed conduit, and a second pump for applying suction continuously to said return conduit at that end which is remote from said nozzle.

Preferably means is provided for varying the pressure of circulating liquid at said nozzle between substantially ambient pressure and a pressure higher than ambient.

The pressure varying means may comprise a reservoir, through which the liquid passes, positioned in said feed conduit and activating means operable to reduce the volume of said reservoir, to displace at least some of the liquid from said reservoir into said feed conduit and thereby increase the pressure of the circulating liquid.

The arrangement is such that the volume of liquid being circulated along said first conduit is in excess of the volume of liquid required for application to the surface through said orifice, so that whilst the circulating means is operating liquid is being fed continuously along both of said conduits.

To allow the liquid to drain into the container when the circulating means are not operating the container may be mounted at a lower level than that of the nozzle and the pressure varying means.

Where however the container is mounted at a higher level than that of the nozzle and the pressure varying means, a closed secondary container may be mounted at a lower level than any other part of the apparatus, said feed and return conduits each being connected separately to said secondary container by a branch conduit, the branch conduit connecting said feed conduit with said secondary container being provided with a control valve operable to enable liquid to flow into said secondary container, under gravity, or to prevent such flow of liquid. With this construction the secondary container may be provided with a vent pipe having a control valve, said valve being operable to open said secondary container to ambient pressure to enable any liquid in the secondary container to be returned by said second pump to said container.

The nozzle may be supported on link means which is so constructed and arranged that the nozzle may be moved by operating means between an idle position and an operating position at which a liquid application is made. In the operating position the nozzle may for example be adjacent to a conveyor or other feed means carrying a carton blank or the like, so that liquid from the nozzle may be applied to the surface of the said blank, whilst in the idle position the nozzle may be withdrawn clear of said conveyor.

In a preferred form the link means is in the form of a parallelogram linkage comprising a movable plate on which said nozzle is fixed, said movable plate being supported by a pair of swing arms each of which is pivotally connected at one end to the movable plate and at the other end to a fixed mounting member or members. Said operating means may comprise a cam which contacts a cam follower mounted on a further arm pivotally connected at one end to one of said pair of swing arms, said cam being adapted to cause the nozzle to move towards and away from said operating position..

The said feed and return conduits may comprise flexible tubes connected between said container, and said feed passage and said return passage respectively, but in the preferred form of apparatus each of the flexible tubes is connected, at its end remote from said container, to a series of ducts provided in said fixed mounting member(s), one of said pair of swing arms, and said movable plate, said ducts being so arranged that liquid flows along one series of ducts (feed ducts) to said feed passage in said nozzle, and from said return passage in said nozzle along the other series of ducts (return ducts).

In the preferred form said reservoir comprises a cylindrical chamber in communication with the feed duct in said movable plate, and said activating means comprises a piston movable within said chamber, by a pusher member carried on one of said pair of swing 3 arms, operation of said pusher member being in synchronism with movement of said nozzle by the operating means so that liquid is displaced from said chamber into said feed duct each time said operating means causes said nozzle to move to said operating position.

Where said ducts pass through the pivotal connection at each end of said one of said pair of swing arms, the ducts are arranged so that said pivotal connections are lubricated by the liquid as it flows along the ducts.

In apparatus where linesof liquid, having a finite length, are required to be applied at intervals to a continuous surface or to a succession of carton blanks, fed intermittently past the nozzle, the nozzle may comprise a box-like member'having an orifice in the form of a straight slot, formed in one face thereof, and a partition, inside said member to form first andsecond compartments therein, one edge of said partition being directly opposite said orifice and spaced from the inner surface of said one face of said member, wherein said first compartment is connected to said feed conduit, said second compartment is connected to said return conduit, said one edge of said partition forming a weir over which liquid flows from said first to said second compartment.

Where a succession of dots, or a broken'line, of liquid is required to be applied to a surface being fed past the nozzle, the nozzle may comprise an inner and outer tube, said outer tubebeing positioned round and coaxial with said inner tube, the cross-sectional dimensions of the tubes being such that a space is formed within said outer tube and surrounding said inner tube, wherein one end of said inner tube is connected to said feed conduit, the corresponding end of said outer tube is connected to said return conduit, the end of the wall of the inner tube,remote from said one end, forming a weir over which liquid flows from said inner tube into said space surrounding said inner tube. The said inner tube may be tube.

The remote end of said outer tube projects beyond the corresponding end of the inner tube so that liquid does not flow beyond the end of the outer tube except when the liquid pressure at said nozzle is higher than ambient. The nozzle may be moved between'the idle position and the operating position, and adhesive caused to flow from the nozzle when it is in the operating position, byv variation of pressure as previously described.

(With the last-mentioned form of nozzle, for any particular setting of said first and second pumps liquid may be caused to flow continuously out of the end of said outer tube remote from said one end by suitably adjusting the position of the said remote end of the inner tube relative to that of the outer tube. In this case no reser voir is rquiredin-said feed conduit).

When the liquid to be applied to the surface has a very low viscosity then a secondary nozzle having a single interior compartment is connected into said return conduit at a point where the pressure within said return conduit is below ambient pressure.

Although as indicated above the apparatus may be used for the application of liquids generally, its preferred use is in the application of flowable adhesives.

It will be obvious that if a hot melt adhesive is being applied to the surface the link means requires to be heated so as to keep the adhesive in a fluid state.

axially adjustable relative to said outer Preferred forms of apparatus will now be described, I

byway of example only, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic showing of apparatusfor applying adhesive to a surface,

FIG. 2 is a view similar to FIG. 1 but showing a modified form of apparatus,

FIG. 3 is a view of a part of the apparatus of FIG. 1 but showing a further modification,

FIG. 4 is a front elevation of apparatus according to the invention for applying adhesive to a surface,

FIG. 5 is a view, partly in section, taken in the direction of arrow A of FIG. 4,

FIG. 6 is a section on the line Vl-'VIof FIG. 4,

FIG. 7 is a section on the line VII-VII of FIG. 5,

FIG. 8 is a sectional view of a modified form of applicator nozzle, and a FIG. 9 is a plan view of the nozzle of FIG. 8.

Referring first to FIG. 1, the apparatus shown comprises an adhesive container 1, in which a feed pump 2 is located, and having a feed conduit 3 extending to an applicator nozzle 4. A return conduit 5 extends from the nozzle 4 back to the reservoir 1, being connected to a return pump 6 also located in said container. The pumps 2, 6 are shown diagrammatically, but it will be understood that the feed pump 2 has an inlet open to receive adhesive from a supply in the container 1, and

i an outlet which is connected to the conduit 3, while the return pump 6 has an inlet connected to the conduit 5 and an outlet open to discharge returned adhesive into the container.

A device 7 for varying the pressure of adhesive in the feed conduit 3 is connected to said conduit, between the pump 2 and the nozzle 4 and said device 7 comprises a short cylinder 8 communicating with the conduit 3, and a piston 9 slidable in the cylinder'8.

The nozzle 4 includes a discharge orifice 10 connected by a feed passage 11' to the feed conduit 3, and a return passage 12 connecting said orifice 10 to the return conduit '5.

In operation, the pumps 2, 6 operate continuously and adhesive is pumped away from the container 1 through the feed conduit 3 and back to the container 1 through the return conduit 5. As long as the piston 9 is stationary, whatever its position, the pressure of ad-' hesive in the feed conduit 3 is somewhat higherthan ambient pressure, while the pressure in return conduit 5 is somewhat lower than ambient pressure, and the characteristics of the two pumps 2, 6 and the layout of the conduit 3, 5 are such that in these circumstances the pressure of adhesive immediately inside the orifice 10, where adhesive fed through the feed passage 11 leaves that passage and enters the return passage 12, issubstantially equal to the ambient pressure, so that there is nothing to cause adhesive to be impelled outward through theorifice 10. While these conditions persist, the piston 9 is normally maintained in a raised position in its'cylinder 8, by a spring (not shown), so that the part of the cylinder below the pistonis full of adhesive. When it is desired to cause adhesive to be expelled through the orifice 10, the piston 9 is depressed, that is, moved towards the conduit 3, thus driving out adhesive from the cylinder 8 into the conduit 3 and increasing the pressure in that conduit. This alters the pressure conditions in the adhesive circuit formed by the conduits 3, 5 and the container 1, and the pressure of the adhesive at the inner end of the orifice 10- increases slightly; this change is sufficient to cause adhesive to be expelled through said orifice. Thus with the apparatus shown in FIG. 1, adhesive may be expelled through the orifice at any time by operation of the piston 9, and the rate at which adhesive is thus expelled will depend upon the speed with which the piston 9 is depressed. As soon as downward motion of the piston 9 stops, so does the emission of adhesive from the orifice l0 cease, and the maximum quantity that can be thus emitted without interruption is equal to the capacity of the cylinder 8 below the piston 9, when the latter is in its uppermost position.

The nozzle 4 may if desired be a multiple nozzle, that is, it may be elongated in a direction at right angles to the plane of the drawing, and the orifice 10 may be in the form of an interrupted slot or a number of discrete holes, or the orifice 10 may be a single elongated slot so that a line of adhesive is deposited on any surface which may be placed adjacent to said orifice.

Further nozzles may be supplied, if desired, from the same container 1 and pumps 2, 6, and the dashed lines indicate what is necessary if a second, independentlyoperable nozzle is to be provided. As will be seen from the figure, a branch 3a of the feed conduit 3 is connected to a second nozzle 4a and a branch 5a connects said nozzle 4a to the return conduit 5. A device 7a (similar to the device 7) is connected to the branch feed conduit 3a, and between the point at which the branch conduit 3a leaves the main feed conduit 3 and the respective devices 7, 7a there are provided nonreturn valves 13, 13a. With these added elements in the apparatus of FIG. 1, it will be understood that adhesive may be expelled from the nozzle 4 or the nozzle 4a as desired, by depression of the piston of device 7 or that of device 7a, respectively, and whenever one of the devices 7, 7a is thus operated, the respective non-return valve 13, 130 respectively will prevent the change in pressure conditions produced by operation of said device from affecting the pressure of adhesive at the other one of the two nozzles.

The container 1 will of course require to be refilled with adhesive from time to time, and for this purpose a filling pipe 14 with a manually operable valve 15 is provided. The valve 15 is kept closed during normal operation, but is opened whenever it is desired to feed further adhesive into the container 1, through the pipe 14. The container 1 may be fitted with any desired form of level indicator (not shown).

The system illustrated in FIG. 1 can be satisfactorily operated so long as the container 1 is at a lower level than the nozzle or nozzles because whenever operation of the system is stopped, the fact that the container is at a lower level than the container means that adhesive remaining in the conduits when the pumps stop can drain back into the container purely by gravity. When however the container is at a higher level than the nozzle or nozzles, the nozzles and conduits remain filled with adhesive when the pumps stop, and with many adhesives (especially hot melt adhesives) this creates a problem when it is desired to restart the system. In FIG. 2 there is illustrated apparatus generally similar to that of FIG. 1, but including provision to deal with this problem.

As seen in FIG. 2, much of the apparatus is just as shown in FIG. 1 and these parts are given the same references as in FIG. 1 and the description of them will not be repeated. It is noted however that in FIG. 2 the disposition of the parts is different in that the nozzle 4 is at a lower level than the container 1, thus in the absence of the additional equipment about to be described, creating the problem explained above.

Additionally, however, in the apparatus of 'FIG. 2 there is a secondary container 16 connected to the feed conduit 3 by a branch 3b and to the return conduit 5 by a branch 5b. This secondary container 16 is at a lower level than any other part of the apparatus, and it is provided with a vent pipe 17 having a control valve 18 by which the container 16 may be opened to the ambient air. A valve 19 is provided in the branch conduit 3b.

In normal operation, the apparatus of FIG. 2 operates as described above with reference to FIG. 1, provided the valves l8, 19 are both closed. When operation of the apparatus ceases, and the pumps 2, 6 are stopped, the valve 19 is opened and left open, so that adhesive remaining in the conduits 3, 5, in the device 7, and in the nozzle 4 can drain into the secondary container 16 under the influence of gravity. When the apparatus is to be restarted, the valve 19 is closed and the valve 18 opened, and this allows the adhesive collected in the container 16 to be returned to the container 1 by the return pump 6. It will be appreciated that, for this operation to take place satisfactorily, the vent l7, container 16, and branch conduit 5b must provide a somewhat less restricted passage than the parallel part of the main adhesive circuit, containing the nozzle 4.

Apparatus such as that shown in FIG. 1 and FIG. 2 is well adapted for use with hot melt adhesives, where it is of particular advantage to employ a system in which adhesive is circulated continuously because of the need to maintain the temperature of the adhesive above a certain minimum level to keep it in a sufficiently fluid state. Where apparatus as shown in either of these figures is to be used with hot melt adhesive, it will be appreciated that heating devices and possibly heat insulation will be provided in suitable places.

In the apparatus shown in FIG. 1 and that shown in FIG. 2, the pressure of the adhesive at the inner end of the orifice in the nozzle is substantially equal to the ambient pressure when adhesive is not being emitted through the orifice, and is slightly higher when adhesive is being so emitted. In the return conduit 5, the pressure is lower than the ambient pressure, and this fact may be utilised when it is desired to provide for the removal of excess ahesive from any surface to which it may be applied via the nozzle 4. FIG. 3 is a fragmentary view of a suitable arrangement for this purpose, and it will be seen that in FIG. 3 there is shown the nozzle 4 with its orifice 10, a portion of the feed conduit 3, and a portion of the return conduit 5. In the portion of return conduit 5 which is shown, it will be seen that there is also a secondary nozzle 20, and also in FIG. 3 there is shown a moving web 21 of, for example, a wrapping material, travelling in the direction indicated by the arrow so that it passes first the nozzle 4 and then the secondary nozzle 20. The nozzle 20 comprises a simple hollow body, communicating with the return conduit 5 at one end and having an orifice 22 at the other end across which the web 21 runs.

With the arrangement shown in FIG. 3, when any particular area of the web 21 has received adhesive from the nozzle 4, as it passes over the secondary nozzle 20 it is exposed to a degree of suction, due to the slightly lower pressure in the return conduit 5, and this suction tends to remove some of the adhesive previously applied to the web 21. This arrangement is most useful with adhesives (or other coating liquids) of low viscosity and the extent to which adhesive (or other liquid) previously applied to the web is removed by the nozzle 20 depends upon the positioning of the nozzle relative to the web and the size of the orifice 22. The operation is also of course affected by the magnitude of the pressure drop in that part of the conduit between the two nozzles 4, 20, and if it is desired to increase this pressure drop then this of course may be effected by making this part of the return conduit of smaller diameter.

Reference will now be made to FIGS. 4 7 which show apparatus for applying four lines of adhesive, as will be described later, to'a succession of carton blanks being fed intermittently in the direction of arrow B, by any convenient known type of conveyor (not shown). A part of one such carton blank is shown at CB in FIGS. 4, 5 at the position at which adhesive will be applied to it.

An applicator head, indicated generally at 23, comprises a block 24, which as viewed in FIG. 5, has a horizontal cross piece 29 and a central piece 30 extending vertically downwards therefrom. On each end of the cross piece 29 there is mounted a pair of adhesive applicator nozzles 25, 26 and 27, 28 respectively. The block 24 is mounted on a parallelogram linkage, generally indicated at 31, which comprises a movable plate 32, to which the block 24 is fixed; an upper swing arm 33, and a lower swing arm 34 which is formed as a triangular plate; and a fixed plate 35 and a bracket 36. The plate 35 is attached to a further plate 37 which is in turn attached to a fixed part 38 of the apparatus to which the bracket 36 is also attached. One end of the upper swing arm 33 is pivotally connected at 39 to the plate 32 and the other end is pivotally connected at 40 to the plate 35. The lower swing arm 34 is pivotally connected at 41 to the plate 32 and at 42 to the bracket 36. The arrangement is such that the pivots 39, 40, 41, 42 are at the corners of the parallelogram linkage 31.

The lower swing arm 34 is also pivotally connected at 43 to one end of a connecting arm 44 which extends from the connection 43 through a hole in the fixed part 38 of the apparatus. The arm 44 is supported near its other end by a block 45, which engages in a slot 47 in the arm 44, and which is loosely mounted on a rotatable shaft 46. Fixed to the shaft 46 are two cams 47, 48, mounted on opposite sides of the arm 44, which engage cam followers 49, 50 respectively, the latter being rotatably mounted on the arm 44.

Fixed to the plate 35 is a manifold block 51 and fixed to the swing arm 34 is a bracket 54 having an angled projection 55.

The applicator nozzles 25 28 may be supplied with adhesive in the same way as that described, with reference to FIG. 1, for supplying adhesive to the nozzle 4. For this purpose the manifold block 5] has connected to it a feed conduit 56 (which corresponds to feed conduit 3 of FIG. 1) and a return conduit 57 (which corresponds to return conduit 5 of FIG. I).

During operation of the apparatus, adhesive is pumped along the conduit 56 and into a duct 58 formed in the manifold block SI. Also formed in the block 51 is a cylindrical chamber 59. A piston 60 (FIG. 7) is provided in the chamber 59, and is fixed to one end of a piston rod 61 which extends to the outside of the block 51. The other end of the piston rod 61 is enlarged at 62 and a spring 63 is provided to urge the piston to the position shown in FIG. 7. The piston 60 is movable within the chamber 59 by the angled projection 55 engaging the portion 62 of the piston rod 61.

The adhesive flows from duct 58 into a U shaped channel 64 formed in that face of the plate 35 which abuts the manifold block 51, and the chamber 59 is arranged to be in communication with the channel 64 (FIG. 7), so that the chamber becomes filled with adhesive. Beyond the chamber 59, considered in the direction of flow of the adhesive, the channel 64 becomes a cylindrical duct 64a from which the adhesive flows through the pivotal connection 40 into the upper swing arm 33 as will now be described.

The arm 33 is rotatably mounted at its right hand end, as viewed in FIG. 6, on a fixed central hollow tube 65 (FIG. 6) which is closed at each end, and divided into the two sections 66, 67 by a partition 68, the tube 65 being fixed in a hole provided in the plate 35. The arm 33 has a duct 69 formed in it which communicates with an annular space formed in a tube 71 which is fixed into a hole in the end of the arm 33 and fits over the tube 65. Two holes 72 in the tube 65 provide communication between the space 70 and section 66 of the tube 65.

From the duct 64a the adhesive flows via a hole 73 in the tube 65 into and along the section 66 of the tube 65, through holes 72, space 70 and along duct 69, which extends along the arm 33 to the pivotal connection 39 which is constructed in a similar manner to the pivotal connection 40. In the pivotal connection 39, the arm 30 is rotatably mounted on a fixed central hollow tube 65a which is closed at each end, and is divided into two portions 660, 67a by a partition 68a, the tube 65a being fixed in a hole provided in the plate 32. The duct 69 communicates with an annular space 70a formed in a tube 71a, which is fixed into a hole in the end of the arm 33 and fits over the tube 65a. Two holes 72a in the tube 65a provide communication between the space 700 and portion 660 of the tube 650.

From the duct 69 the adhesive flows through the space 70a, holes 72a and portion 66a of the tube 650 into a duct 74 formed in the plate 32, via a hole 73a in the tube 65a. From the duct 74 the adhesive flows along a duct 74a formed in the cross piece 29 of the block 24 and then into the nozzles 25 28. As the nozzles are arranged in pairs, and the pairs are similar in construction, only nozzles 27, 28 will be described in detail.

The nozzles 27, 28 comprise an inner plate 75, an outer plate 76 and a central plate 77. Between the plate and the plate 77 is a thin partition 78 and between the plate 76 and the plate 77 is a thin partition 79. The various parts are so shaped and arranged that discharge orifices 80, 81 are formed at the upper end of the nozzles 27, 28 respectively, and the spaces between the plates 75, 77 and 76, 77 are each divided into two compartments 82, 83 and 84, 85 respectively. The upper ends of the partitions 78, 79 terminate adjacent to the orifices 80, 81 respectively. The adhesive flows from the duct 74a into the compartments 82, 85, over the tops of the partitions 78, 79 and into the compartments 83, 84.

Adhesive is supplied to and returned from the nozzles 25, 26 via duct 74a and return passage 86 respectively,

which are connected to compartments in nozzles 25, 26 corresponding to the compartments 82, 83, 84, 85, of nozzles 27, 28.

Whilst flowing along the various ducts so far described the adhesive has been subjected (as described with reference to FIG. 1) to a pressure higher than ambient pressure, which in this particular case is atmospheric, so that until it reaches the orifices 80, 81 the adhesive is subjected to a pressure higher than atmospheric pressure.

As previously mentioned with respect to FIG. 1, the adhesive is continuously circulated to and from the container 1. The return path of the adhesive in the apparatus of FIGS. 4 7 will now be described, but as it is basically the same as the feed path described above, but the flow is in the opposite direction, it will not be described in such great detail.

The return flow of adhesive is subjected to subatmospheric pressure which is so adjusted relative to the pressure feeding the adhesive to the nozzles 27, 28 that no adhesive is ejected from the orifices 80, 81.

The adhesive flows from the compartments 83, 84 into a passage 86 formed in the cross piece 29 and then into a passage 87 formed in the plate 32. From the passage 87 the adhesive flows through a hole 88a intosection 67a of the tube 65a and through holes 89a into a further annular space 90a formed in the tube 71a. The space 90a communicates with a passage 69a which is formed in the arm 33 and runs parallel with the duct 69. From the passage 690, the adhesive flows into an annular space 90, through holes 89 and into section 67 of tube 65. A hole 88 allows the adhesive to flow along a passage 91, formed in the plate 35, and to the manifold block 51 and thence into the return conduit 57 which corresponds to the return conduit of FIG. 1.

The tube 71 of the pivotal connection 40 is provided with a further annular space 92, positioned on the other side of the annular space 70, and connected to the annular space 90 by a passage 93. With this arrangement the annular spaces not only provide means for guiding the adhesive, but allow the adhesive to act as a lubricant as the tube 71 pivots about the tube 65. It will be noted that the annular space 70 has adhesive flowing through it at a pressure which is higher that the adhesive flowing through the annular spaces 90 and 92 and with normal matching tolerances there will be a slight leakage from space 70 to the spaces 90, 92, this arrangement being similar to that of a hydrostatic bear ing. The other pivotal connection 39 is constructed in the same way so will not be further described.

The operation of the apparatus of FIGS. 4 7 will now be described.

The carton blank CB is brought to rest at a position such that four lines of adhesive may be applied to it by the nozzles 25 28.

Adhesive is being continuously circulated along feed conduit 56 through the internal compartments (e.g. compartments 82, 83) of the nozzles 25 28 and back along return conduit 57 by pumps from a container, (not shown), corresponding to container 1 and pumps 2 and 6 of FIG. 1.

The shaft 46 is continuously rotated and as the cams 47, 48 rotate from the position shown in FIG. 4 they cooperate to move the connecting arm 44 to the right. This causes the swing arms 33, 34 to swing about their respective pivots 40, 42 and the plate 32 and therefore the nozzles 25 28 will be raised from the full line position of FIG. 4 to the position indicated in chain dot lines against the underside of the blank CB.

As the arm 34 swings about its pivot 42 the bracket 54 will move with it and the angled projection 55 is so arranged that it engages the portion 62 of the piston rod 61. On continued movement of the arm 34 the projection 55 causes the piston 60 to move, against the spring 63, so that some of the adhesive in the chamber 59 is displaced into the channel 64, which causes an increase in the pressure of the flow of adhesive between the chamber 59 and the nozzles 25 28. This increase in pressure causes some adhesive to be ejected from all four orifices at the same time on to the bank CB.

On continued rotation of the cams 47, 48 the nozzles are returned to the full line position of FIG. 4 and during this movement the piston will be returned to the position shown in FIG. 7 by the spring 63, as the projection 55 moves out of engagement with the portion 62 of the piston rod 61. The increase in pressure which causes adhesive to be ejected from the nozzles is maintained only whilst the piston is being moved by the projection 55, so the amount of adhesive to be displaced from the chamber 59 equals the amount required to be ejected through the nozzles on to the blank CB. As the piston returns to its original position the chamber 59 refills with adhesive. It should be noted that there is continuous circulation of the adhesive even during application of adhesive to the blank CB.

The apparatus shown in FIGS. 4 7 is particularly adapted for applying hot melt adhesives, and for this purpose the various components have to be heated so that the adhesive remains in a flowable condition. One such heater is for example mounted in the arm 33 at the position indicated by reference 94. When using hot melt adhesive, the nozzles 25 28 (or, at least, those parts of said nozzles in the near vicinity of their orifices) are maintained at a somewhat higher temperature than the remaining parts of the apparatus as this has been found to reduce tailing of adhesive as each ejection from the nozzles stops and the nozzles move away from the blank CB.

Reference will now be made to FIGS. 8 and 9 which show a modified form of applicator nozzle as compared with that shown in FIGS. 4 to 7.

The nozzle comprises two coaxial open-ended cylindrical tubes, namely an outer tube 95, which is fixed at its lower end into a block 96, and an inner tube 97 which is fixed at its lower end into a further block 98, positioned below the block 96.

The inside of the tube communicates with a pas sage 99 in the block 96, and the inside of the tube 97 communicates with a duct 100 in the block 98. The block 96 has formed in it a hole 101 which is coaxial with the tube 95, and has a portion of reduced diameter breaking through into the passage 99 and forming a shoulder 102. A rubber sleeve 103 is positioned in the hole 101 so that it abuts against the shoulder 102 and a bolt 104 is screwed into the hole to retain the sleeve 103. The sleeve 103 and bolt 104 are each provided with a central longitudinal bore. The arrangement is such that the tube 97 extends from the block 98,

through the central bores of the bolt 104 and sleeve 103, the reduced-diameter portion of the hole 101, and into the tube 95 with which it is coaxial.

The blocks 96, 98 may be fixed to a plate 32a having a duct 105 and a passage 106 formed in it. The plate 32a, duct 105 and passage 106 correspond to the plate 32, duct 74, and a passage 87 respectively of FIGS. 4, and 6. It will be .seen therefore that with the nozzle shown in FIGS. 8, 9 mounted as just described, adhesive will flow from feed conduit 56 through the various ducts described with reference to FIGS. 4 to 7, into the ducts 105, 100 and thence along the inner tube 97. The adhesive will then flow over the top of tube 97 into the tube 95, passages 99, 106 and back along the various passages described with reference to FIGS. 4 to 7 to the return conduit 57.

The block 98 is mounted on the plate 32a in such a manner that it, and therefore the tube 97, may be moved so that the tube 97 moves axially relative to the tube 95. In this way the distance between the tops of the tubes 95, 97 may be altered. To allow for this movement of the block 98 the passage 100 is enlarged at 107 so that it is always in communication with the duct 105. A spacer member 108 is provided near the top of the tube 97 so as to keep the tubes coaxial. The member 108 has four cut-outs 109 in its periphery (FIG. 9) to allow the adhesive to flow along the tube 95.

The nozzle shown in FIGS. 8, 9 may be used for either applying a continuous line of adhesive to a surface, or applying spots (or broken lines) of adhesive to a surface.

For applying a continuous line of adhesive to a surface the inner tube 97 is adjusted axially relative to the outer tube 95 so that adhesive will flow continuously out of the top of the outer tube 95 whilst the adhesive is being circulated as described with reference to FIG. 1. In this case however, there is no need for the pressure to be increased as previously described.

The inner tube 97 is moved axially relative to the outer tube 95 by loosening the bolt 104 which allows the sleeve 103 to expand axially and thus lessen its grip on the tube 97, which may now be moved by sliding the block 98 on the block 32a until the desired distance is obtained between the tops of the tubes 95, 97. The bolt is then screwed up which compresses the sleeve 103 against the shoulder 102 and causes the sleeve to grip the tube 97 and prevent it moving axially.

The nozzle may be moved to and from the surface by the apparatus described above with reference to FIGS. 4 and 5 and the ejection of adhesive from the tube 95 will be stopped and started as the circulation of adhesive is also stopped and started.

For applying spots or broken lines of adhesive to a surface the distance between the tops of the tubs 95, 97 is altered, as described above, so that whilst adhesive is being fed to the nozzle at a constant pressure no adhesive will flow out of the tube 95. The nozzle may then be moved to the adhesive applying position and adhesive caused to be ejected from the tube 95 in the same way as described above with reference to FIGS. 4 to 7.

The form of nozzle shown in FIGS. 8 and 9 is especially useful for theapplication of adhesives (or other coating materials) of high viscosity, as the relatively large area of the return passage provided by the annular-section space between tube 95 and tube 97 enables the adhesive (or other material) to pass more readily from the feed duct constituted by the interior of tube 97 to said return passage.

It is noted that in the foregoing description, parts of the feed path of adhesive have been termed ducts while parts of the return path have been termed passages; the use of different terms does not however indicate any structural difference.

We claim:

1. Apparatus for applying a liquid, for example an adhesive or the like, to a surface, comprising a container for the liquid, at least one applicator nozzle, feed and return conduits for conveying liquid from the container to the nozzle and from the nozzle to the container respectively, and means for circulating liquid continuously from the container through said conduits, said circulating means comprising a first pump for feeding the liquid continuously at a predetermined pressure above ambient pressure along said feed conduit and a second pump for applying suction continuously to said return conduit at that end which 'is remote from said nozzle, in which said nozzle has a discharge orifice which is in constant communication with said conduits and is unclosable.

2. Apparatus as claimed in claim 1 in which said nozzle includes separate feed and return passages connected to the feed and return conduits respectively, said passages'being interconnected immediately adjacent to the inner end of the orifice.

3. Apparatus as claimed in claim 1 in which means is provided for varying the pressure of circulating liquid at said nozzle between substantially ambient pressure and a pressure higher than ambient.

4. Apparatus as claimed in claim 3, in which said pressure varying means comprises a reservoir, through which the liquid passes, positioned in said feed conduit and activating means operable to reduce the volume of said reservoir to displace at least some of the liquid from said reservoir into said feed conduit and thereby increase the pressure of the circulating liquid.

5. Apparatus as claimed in claim 4 in which said container is mounted at a lower level than that of the nozzle and the pressure varying means.

6. Apparatus as claimed in claim 4 in which said container is mounted at a higher level than that of the nozzle and the pressure varying means, a closed secondary container being mounted at a lower level than any other part of the apparatus, said feed and return conduits each being connected separately to said secondary container by a branch conduit, the branch conduit connecting said feed conduit with said secondary container being provided with a control valve operable to enable liquid to flow into said secondary container, under gravity, or to prevent such flow of liquid.

7. Apparatus as claimed in claim 6 in which said secondary container is provided with a vent pipe having a control valve, said valve being operable to open said secondary container to ambient pressure to enable any liquid in the secondary container to be returned by said second pump to said container.

8. Apparatus as claimed in claim 7 further comprising link means for movably supporting said nozzle and operating means for moving said nozzle between an idle position and an operating position at which a liquid application is made.

9. Apparatus as claimed in claim 8 in which said link means is in the form of a parallelogram linkage.

10. Apparatus as claimed in claim 9 in which said parallelogram linkage comprises a movable plate on which said nozzle is fixed, at least one fixed mounting member and a pair of swing arms each of which is pivotally connected at one end to the movable plate and at the other end to said fixed mounting member.

11. Apparatus as claimed in claim in which a further arm is pivotally connected at one end to one of said pair of swing arms and said operating means comprises a cam and a cam follower mounted on said further arm, said cam being adapted to cause the nozzle to move towards and away from said operating position.

12. Apparatus as claimed in claim 11 in which said feed and return conduits comprise flexible tubes.

13. Apparatus as claimed in claim 12 in which a series of feed ducts and a series of return ducts are provided in said fixed mounted member, one of said pair of swing arms, and said movable plate, each of the flexible tubes being connected, at its end remote from said container, to one of said series of ducts, said ducts being so arranged that liquid flows along said series of feed ducts to said feed passage in said nozzle, and from said return passage in said nozzle along said series of return ducts.

14. Apparatus as claimed in claim 13 in which said reservoir comprises a cylindrical chamber in communication with the feed duct in said movable plate, and said activating means comprises a piston movable within said chamber by a pusher member carried on one of said pair of swing arms, operation of said pusher member being in synchronism with movement of said nozzle by the operation means so that liquid is displaced from said chamber into said feed duct each time said operating means causes said nozzle to move to said operating position.

' 15. Apparatus as claimed in claim 14 in which the feed and return ducts, where they pass through the pivotal connection at each end of said one of said pair of swing arms, are arranged so that said pivotal connections are lubricated by the liquid as it flows along the ducts.

16. Apparatus as claimed in claim 15 in which said nozzle comprises a box-like member having an orifice in the form of a straight slot formed in one face thereof and a partition inside said member to form first and second compartments therein, one edge of said partition being directly opposite said orifice and spaced from the inner surface of said one face of said member, said first compartment is connected to said feed conduit, said second compartment being connected to said return conduit, and said one edge of said partition forming a weir over which liquid flows from said first to said second compartment.

17. Apparatus as claimed in claim 15 in which said nozzle comprises an inner and outer tube, said outer tube being positioned round and coaxial with said inner tube, the cross-sectional demensions of the tubes being such that a space is formed within said outer tube and surrounding said inner tube, one end of said inner tube being connected to said feed conduit, the corresponding end of said outer tube being connected to said return conduit, and the end of the wall of the inner tube, remote from said one end, forming a weir over which liquid flows from said inner tube into said space surrounding said inner tube.

18. Apparatus as claimed in claim 17 wherein the remote end of said outer tube projects beyond the corresponding end of the inner tube so that liquid does not flow beyond the end of the outer tube except when the liquid pressure at said nozzle is higher than ambient.

19. Apparatus as claimed in claim 17 in which said inner tube is axially adjustable relative to said outer tube.

. I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 1 Robert William Davies and Leonard Thornton It is certified thaterror appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page, column 1, between lines 7 and 8, insert the following:

Foreign Application Priority Data Nov. 26, 1971 Great Britain.......54920/7l Column 1, lines47 52, cancel:

"In a preferred form .length of the nozzle."

Column 12,; line 4, to Column 14, line 34, ancel in their entirety and substitute the following:

--l. Apparatus. for applying a liquid,- for example an adhesive or thelike, to a surface, comprising a container for the liquid,v at least one applicator nozzle,y-feed and return conduits for conveying liquid from the container to the nozzle and from the nozzle to the container respectively, and means for circulating liquid continuously from the container through said conduitsb said circulating means. comprising a first pump for feeding the liquid continuously at a predetermined pressure above ambient pressure along said feed-conduit and a second pump for applying suction-continuously to said return conduit at that end which is remote from said nozzle, in which said nozzle comprises a'discharge orifice which is" uncl osable and separate feedfand' return passages connected-to the feed and return conduits respectively so that said orifice is in constant communication with said conduits said passages being FORM PO- I USCOMM-DC 5037:: F69- GOVERNMENT PRINTING OFFICE: I969 0-366-334 -2- A A UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,815,822 Dated 'June ll, 1974 Robert William Davies and Leonard Thornton It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

interconnected immediately adjacent to the inner end of the orifice.

2. Apparatus as claimed in claimfll in which means is provided for varying thepressure of circulating liquid at said nozzle between substantially ambient pressure and a pressure higher than ambient. A

q 3'. Apparatus as claimed in claim 2, inwhich said pressure varying means comprises a reservoir, through which the liquid passesfpositioned in said feed conduitjiand activating means operable to reduce the volume of said reservoir to displace at least some of the liquid from said reservoir into said feed conduit and thereby increase the pressure of the circulating liquid. I 1

I 4. Apparatus as claimed inclaim 3 in which said container is mounted at a lower level than that of the nozzle and the pressure varying means.

5. Apparatus as claimed in claim 3 which said container is mounted at a higher level than that of the nozzle and the pressure varying means, a closed secondary container being mounted at a lower level than any other part of the apparatus, said feed and return conduits each being connected separately to said secondary container by a branch conduit, the branch conduit connecting said feed conduit with: said secondary container being provided with a control valve, operable .to enable liquid to flow into said secondary container, under gravity, or to prevent'such flow of liquid. A}

F ORM PO-1050 (IO-'69) USCQMM-DC 6O376-P69 u.s. GOVERNMENT PRINTING OFFICE Isis o-ass-su v: 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,815,822 Dated June 11', 1974 Inventor) Robert William Davies and Leonard Thornton It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

6. Apparatus as claimed in claim 5 in which said secondary container is provided with a vent pipe having a control valve, said; valve being operable to open said secondary concontainer to be returned bysaid second pump to said container.

7. Apparatus as claimed in claim 6 further comprising link means for movably'supporti'ng said nozzle and operating means for moving} said; nozzle between idle position and an operating position at which a liquid application is made.

. 8. Apparatus as claimed in claim 7 in which said link means is in the form of a parallelogram linkage.

9. Apparatus as claimed in claim 8 in which said parallelogram linkage comprises a movable plate on which said nozzle is fixed, at least one fixed mounting member and a pair of swing arms each of which is pivotally connected at one end to the movable plate and at the other end to said fixed mounting member. I

10. Apparatus as claimed in claim 9 in which a further arm is pivotally connected at one end to one of said pair of swing arms and said operating means comprises a camand' a cam followermoun-ted on said further arm, said cam being adapted t1 cause the nozzle to move towards and away from said operating position.

11. Apparatus as claimed in claim 10 in which said feed and return conduits comprise flexible tubes.

F ORM PC4050 (IO-69) USCOMM-DC suave-ps9 LIQS G OVERNMENT PRINTING OFFICE I969 O3i6-33| tainer to ambient pressure to enable any liquid in the secondar PatentNo. 1 2 Da e June 11, 1974 Inventor) Robert William Davies and Leonard Thornton It is certified that:- error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

l2. Apparatus as claimed in claim 11 in which a series of feed ducts and a series of return ducts are provided in said fixed mounting member, one of said pair of swing arms, and saidmovabl'e. plate, each ofthe flexible tubes being connected, at its end remote from said container; to one of said series of ducts, said ducts being so arranged that liquid flows along said series of feed ducts to said feed passage in said nozzle, and fromsaid return passage in .said nozzle along said series of return ducts. I

' 13. Apparatus as claimed in claim 12 I inwhich said reservoir comprises a cylindrical chamber in communication with the feed duct in said movable plate, and said activating means comprises a piston movable within saidrchamber by a. pusher-member carried on one of said pair of swing arms, operation of saidpusher member being in synchronism with movement of said nozzle by the operating. means so that liquid is displaced from said chamber into said feed duct each time said operating means "causes said nozzle to move to said operating position. 5

14. Apparatus as claimed in claim- 13 in which the feed and return ducts, where they pass through the- 'pivotalconneetion at' each'end of said one of said pair of swing arms, are arranged's o that said pivotal connections are lubricated by the liquid as it flows along the ducts. 15. Apparatus as claimed in claim 14 infwhich said nozzle comprises-a box-like member having anjor ifice in the form ofa straight slot formed in one face thereof and a F ORM PO-IOSO (10-69) Q I I I Uscowuwoc 50376-969 UIS. GPVERNNENT PRINTING OFFICE: '9! 0-355-33 to said feedv conduit, said second compartment being con [second compartment.

nozzlecomprises' an inner and 0 being positioned round and coaxi 5 .I I v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION June 11, 1974 Patent No. 8-15! 822 Dated Inventor) Robert-William Davies and Leonard Thornton It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ition inside said member to form first and second compartments therein, one edge of said partition being directly' opposite said orifice and spaced from the inner surface of said I one face of said member, said firstcompartment is connected nected to said return conduit, and said/one edge of said partition forming a weir over wh part 16. A ara us as 'claimedin' claim 14 in fwhich said utertube, saidIou-ter tube al with said inner tube, the cross-sectionalidimensions of the tubes being such that a space is formed'within said outer tube-and surrounding said inner tube, one" end of said inner tube being '.connected to said feed conduit, the'corresponding end of sai'd'outer tube being connected ftO said return conduit, and. the end of the wall of the inner tube, remote fromsaid one end, forming a weir over which liquid flows from said inner tube into said space surrounding said inner tube.

\ 17. Apparatus as claimed in claim 16 wherein the 'remoteend of said outer tube projects beyondf'the' corresponding end of the inner tube so that liquid does not r'low beyond .the end of the outer tube except when the liquid pressure at said, nozzle is higher than ambient. 1

Apparatus as claime Signed and sealed this 7th jdayor .iahuary 1975.

QLAL

Atte'st:

' c MARSHALLTDANN Y missifis; of Patents j MCCOY M.- GIBSON-JR, Attesting, pfii'cer ich' liquid flows from said "first to said d in claim l6 i'n which said inner tube is axially-"adjustable relative to said outr. tube. 

1. Apparatus for applying a liquid, for example an adhesive or the like, to a surface, comprising a container for the liquid, at least one applicator nozzle, feed and return conduits for conveying liquid from the container to the nozzle and from the nozzle to the container respectively, and means for circulating liquid continuously from the container through said conduits, said circulating means comprising a first pump for feeding the liquid continuously at a predetermined pressure above ambient pressure along said feed conduit and a second pump for applying suction continuously to said return conduit at that end which is remote from said nozzle, in which said nozzle has a discharge orifice which is in constant communication with said conduits and is unclosable.
 2. Apparatus as claimed in claim 1 in which said nozzle includes separate feed and return passages connected to the feed and return conduits respectively, said passages being interconnected immediately adjacent to the inner end of the orifice.
 3. Apparatus as claimed in claim 1 in which means is provided for varying the pressure of circulating liquid at said nozzle between substantially ambient pressure and a pressure higher than ambient.
 4. Apparatus as claimed in claim 3, in which said pressure varying means comprises a reservoir, through which the liquid passes, positioned in said feed conduit and activating means operable to reduce the volume of said reservoir to displace at least some of the liquid from said reservoir into said feed conduit and thereby increase the pressure of the circulating liquid.
 5. Apparatus as claimed in claim 4 in which said container is mounted at a lower level than that of the nozzle and the pressure varying means.
 6. Apparatus as claimed in claim 4 in which said container is mounted at a higher level than that of the nozzle and the pressure varying means, a closed secondary container being mounted at a lower level than any other part of the apparatus, said feed and return conduits each being connected separately to said secondary container by a branch conduit, the branch conduit connecting said feed conduit with said secondary container being provided with a control valve operable to enable liquid to flow into said secondary container, under gravity, or to prevent such flow of liquid.
 7. Apparatus as claimed in claim 6 in which said secondary container is provided with a vent pipe having a control valve, said valve being operable to open said secondary container to ambient pressure to enable any liquid in the secondary container to be returned by said second pump to said container.
 8. Apparatus as claimed in claim 7 further comprising link means for movably supporting said nozzle and operating means for moving said nozzle between an idle position and an operating position at which a liquid application is made.
 9. Apparatus as claimed in claim 8 in which said link means is in the form of a parallelogram linkage.
 10. Apparatus as claimed in claim 9 in which said parallelogram linkage comprises a movable plate on which said nozzle is fixed, at least one fixed mounting member and a pair of swing arms each of which is pivotally connected at one end to the movable plate and at the other end to said fixed mounting member.
 11. Apparatus as claimed in claim 10 in which a further arm is pivotally connected at one end to one of said pair of swing arms and said operating means comprises a cam and a cam follower mounted on said further arm, said cam being adapted to cause the nozzle to move towards and away from said operating position.
 12. Apparatus as claimed in claim 11 in which said feed and return conduits comprise flexible tubes.
 13. Apparatus as claimed in claim 12 in which a series of feed ducts and a series of return ducts are provided in said fixed mOunted member, one of said pair of swing arms, and said movable plate, each of the flexible tubes being connected, at its end remote from said container, to one of said series of ducts, said ducts being so arranged that liquid flows along said series of feed ducts to said feed passage in said nozzle, and from said return passage in said nozzle along said series of return ducts.
 14. Apparatus as claimed in claim 13 in which said reservoir comprises a cylindrical chamber in communication with the feed duct in said movable plate, and said activating means comprises a piston movable within said chamber by a pusher member carried on one of said pair of swing arms, operation of said pusher member being in synchronism with movement of said nozzle by the operation means so that liquid is displaced from said chamber into said feed duct each time said operating means causes said nozzle to move to said operating position.
 15. Apparatus as claimed in claim 14 in which the feed and return ducts, where they pass through the pivotal connection at each end of said one of said pair of swing arms, are arranged so that said pivotal connections are lubricated by the liquid as it flows along the ducts.
 16. Apparatus as claimed in claim 15 in which said nozzle comprises a box-like member having an orifice in the form of a straight slot formed in one face thereof and a partition inside said member to form first and second compartments therein, one edge of said partition being directly opposite said orifice and spaced from the inner surface of said one face of said member, said first compartment is connected to said feed conduit, said second compartment being connected to said return conduit, and said one edge of said partition forming a weir over which liquid flows from said first to said second compartment.
 17. Apparatus as claimed in claim 15 in which said nozzle comprises an inner and outer tube, said outer tube being positioned round and coaxial with said inner tube, the cross-sectional demensions of the tubes being such that a space is formed within said outer tube and surrounding said inner tube, one end of said inner tube being connected to said feed conduit, the corresponding end of said outer tube being connected to said return conduit, and the end of the wall of the inner tube, remote from said one end, forming a weir over which liquid flows from said inner tube into said space surrounding said inner tube.
 18. Apparatus as claimed in claim 17 wherein the remote end of said outer tube projects beyond the corresponding end of the inner tube so that liquid does not flow beyond the end of the outer tube except when the liquid pressure at said nozzle is higher than ambient.
 19. Apparatus as claimed in claim 17 in which said inner tube is axially adjustable relative to said outer tube. 